1. Field of the Invention
The present invention relates generally to data storage devices and particularly to an improved format for a randomized data block.
2. Background of the Invention
Most modern tape and disk storage devices record data in blocks of information. These blocks are often randomized in order to meet recording constraints. If the blocks are not randomized, particular run lengths may occur in the blocks that would increase the likelihood of recording and read back errors.
FIG. 1 is a block diagram of a format 100 for a randomized data block in accordance with the prior art. The data block format 100 includes a randomizer seed field 102, an ID field 104, an ID field CRC 106, a data field 108, and a block error detection and correction (EDC) field 110. Randomizer seed field 102 is a particular width and is used to store a randomizer seed. The randomizer seed is a random number that is sized to occupy the entire width of randomizer seed field 102.
ID field 104 is used to store an identifier for the data that will be stored in data field 108. An ID field error checking character, such as a CRC, will be generated using the identifier that is stored in ID field 104. The ID field CRC will be stored in its own field, ID field CRC field 106. ID field CRC is used as an additional layer of error checking in order to ensure that the identifier that is stored in ID field 104 is correct. It is very helpful to know whether the identifier stored in ID field 104 is correct prior to getting the data from data field 108. Using an incorrect identifier can create many problems. For example, if the identifier is an address into memory, it is important to make sure the address is correct before altering a memory location.
A block error detection and correction character (EDC) field 110 is also included in the data block. The block EDC is used to detect and correct errors that might occur in the entire data block.
The prior art data block is generated as follows. Data is received and stored in data field 108. An identifier is received and stored in ID field 104. An ID field CRC is generated using the identifier stored in ID field 104. The ID field CRC is then stored in ID field CRC field 106.
A random number is generated that will be used as the randomizer seed. Randomizer seed field 102 is a particular width. The random number that is generated will be this same particular width in order to occupy the entire randomizer seed field 102. The random number is then stored in the randomizer seed field 102.
The combination of the identifier stored in ID field 104, the CRC stored in ID field CRC field 106, and the data stored in data field 108 are randomized using the random number stored in randomizer seed field 102. Error detection and correction is then performed to generate an EDC over the combination of the random number stored in randomizer seed field 102, the identifier stored in ID field 104, the CRC stored in ID field CRC field 106, and the data stored in data field 108. The generated EDC is then stored in block EDC field 110.
The prior art provides for a data block format that includes a separate field for storing the ID field CRC. The separate field is added to each data block. As the amount of data to be stored increases, a larger portion of the storage device must be devoted to providing this separate field for every data block.
Therefore, the current technology would be improved by reducing the size of each data block by utilizing a format for storing a randomized data block that does not require separate space for storing an identifier error checking character.